Icom ID-50A Manual page 11

Lab Notes: GQ Electronics EMF-390 Multi-Field, Multi-Function EMF Meter and RF Spectrum
Power Analyzer
Although the text of the review makes it clear that this
instrument­cannot­be­used­to­accurately­measure­field­
strength, because the manufacturer's documentation
makes reference to EMF exposure, the ARRL Lab took
a closer look at this instrument and its accuracy, or,
more correctly, its lack of accuracy.
The author of this review had initially hoped that this
instrument could be used to perform the required RF-
exposure calculation for his station. He was ultimately
disappointed. He did a calculation of the needed compli-
ance distances, using the ARRL RF Exposure Calcula-
tor found at www.arrl.org/rf-exposure. The calculator
showed him that on 7 MHz, even at 1000 W of SSB,
exposure to neighboring properties was under the limits
(see Figure A).
So far, so good! He then used the instrument to make a
measurement of the power density near the end of his
inverted- end insulator. The instrument gave a reading
V
that was approximately 30 dB lower than the expected
levels, based on the ARRL calculator.
This­raised­red­flags,­so­I­quickly­got­out­my­laptop­
and used my favorite RF tool for all things antenna-
14/04/2024 17:52
Figure A
RF Exposure Calculator
Parameters
This calculator should not be used for antennas that are less than 20 cm (8 in) from a person.
Results for a controlled environment:
Maximum Allowed Power Density (mW/cm
Minimum Compliance Distance (feet):
Minimum Compliance Distance (meters):
For an uncontrolled environment:
Maximum Allowed Power Density (mW/cm
Minimum Compliance Distance (feet):
Minimum Compliance Distance (meters):
Technology
EXPLORE ARRL
50 June 2024 QST www.arrl.org
Power at Antenna:
1000
Mode duty cycle:
Conversational SSB, no speech processing (mode duty cycle=20%)
Transmit duty cycle: (time transmitting)
You transmit for minutes then receive for
5
Antenna Gain (dBi):
2.15
Operating Frequency (MHz):
Include Effects of Ground Reflections
>> Radio Technology Topics
related — EZNEC. (EZNEC can now be downloaded free
of charge at www.eznec.com.)­The­near-field­calculator­
that is part of EZNEC showed results that reasonably
closely agreed with the ARRL RF Exposure Calculator,
with­field­strengths­and­near-field­equivalent­power­den-
sity nowhere near the obviously low reading that the
instrument provided.
Field strength and power density can be measured, but
instruments capable of providing accurate results cost
many thousands of dollars. There are many inexpensive
"EMF" instruments in the marketplace, and the ARRL
Lab does not know of a single instrument costing less
than $1000 that is accurate enough to assess RF expo-
sure. Although the FCC would permit amateurs to make
measurements to assess RF exposure, this instrument
will­not­fit­the­bill.­Amateurs­should­use­the­ARRL­RF­
Exposure Calculator, which gives "worst-case" results for
all but very small antennas, such as 1-meter mag loops,
or use a more accurate calculator, such as EZNEC, to
ensure that their stations can be operated safely. — Ed
Hare, W1RFI, ARRL Lab Volunteer
RF Exposure Calculator
(watts)
minutes (and repeat).
10
7.0
2
):
18.3673
1.8068
0.5507
2
):
3.6735
2.5551
0.7788
>> Safety >> RF Exposure >> RF Exposure Calculator
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